This guide assumes basic knowledge of the the astral system.
The Astral System Guide is a good starting point if you need a quick refresher.

To give credit where it’s due, all astral stats used in my calculation are obtained from the Wartune Wiki, which itself is an excellent resource on the game mechanism.

Is it better to sell all (including unused Oranges), to keep all non-grey, or somewhere in between?

Astral Color

Exp gained

Sells for

Gold/exp

Green

10

3600

360

Blue

30

6000

200

Purple

50

8400

168

Orange

70

10800

154

Red

90

13200

147

What this table shows is that it costs a lot more gold to gain exp from green astrals than from blue ones. Every 1 exp point you get from a green astral costs you 360 gold, wheres a red one only costs you 147 gold per exp point.

Therefore, if you are just starting out, it may be better to sell all until you find (or exchange for) the astral type and color that you desire. Once you have decent starting astrals, you will be better off selling Green ones as they are not cost-effective to engulf. Whether to engulf or sell blue ones really depend on your individual situation, e.g. how much gold you’re making, how much gold you project to need in the near future, and so on.

Is there a method to increase chance of getting orange/red astrals?

One trick that I hear many people swear by is clicking the respective Astro when the corresponding constellation lights up.
Another is to always leave an Astral Star trail, meaning if the fourth one (Saturn) is enabled, you do not click that right away, but click from the start again (Magus) until you get the third (Pallus) enabled; the thought is that if Saturn fails, you can restart from Pallus and not from Magus.
Third one that I hear is to hold your mouse button after you click a Star, count “one-Mississippi”, and let go. Count up to “five-Mississippi” for fifth Star (Chiron).

You may have heard other tricks besides those I mentioned. Whatever the trick you employ, I do not believe it will give you a better chance than mindless clicking. Though if you believe a certain method always works for you, I will not discourage you from continuing to do so.

What astrals are best for me at my level?

Most of the time you can’t go wrong with the 3 “core” astrals: 1 atk and 2 def.
From here the path varies depending on your individual build and situation. There is no universal recommendation that works for everyone all the time.

Ideally, you’d want to use different astrals for the different situation in the game. For example, Sniper’s Edge and Determination for WB; Aegis for Catacomb, Guardian Angel when facing an archer, and so on.

Let’s start with comparison similar astrals. I am using Orange astrals as the basis for all comparisons, and when not specified otherwise I assume 5000 damage done to you, and 5000 damage dealt by you.

Aegis Major vs Goddess Blessings

Aegis reduces damage done to you by an absolute value of 40 / lvl, whereas Goddess reduces by 3% / lvl.
As we can see, this is straightforward, the break even point happens at 1333 damage done to you (1333 x 3% = 40). Therefore, at lower level, Aegis is the better option, and you should switch to Goddess at a level where you receive more than 1333 damage.
Note that you cannot equip both of these Astrals.

Blessed Health vs Regeneration

Another easy one. Blessed heals 400 health / lvl, and Regen heals 10% / lvl of your damage dealt. Each has 10% chance to trigger.
The break even point is then 4000 damage dealt. If you deal higher damage than that, go with Regen, otherwise Blessed.

Enshieldment vs Illusion

Enshieldment adds 216 block points every level. According to Wartune Wiki, each point in block adds approximately 0.04% chance to block an attack.

Assuming no other source of blocks, a level 10 Enshieldment gives you 2160 points or 66% chance to block an attack.
By observation from WB damage, blocked attack reduces damage received by approximately 40%.

This is where the comparison gets tricky.
Illusion treats each part of a multi-attack (such as Mage’s RoF, Knight’s Delphic, Archer’s Multi) as an independent attack. Therefore if a Mage does RoF to you, you could dodge one but not the other.
Block treats all component of multi-attack as one, you either block all or block none.

Illusion reduces all damage done to you to 1, regardless of the type of damage, it could be a critical, normal, or a blocked one.

By observation, a critical hit cannot be simultaneously a blocked one, vice versa. It is not known (at least not to me), whether the game calculates critical first or block first. To move forward, let’s assume for now that block is calculated first before critical (except for archer’s multi-shot where it is always critical).

Going back to our assumption of 5000 damage done to you, you have an expected damage reduction of 1321 (66% x 5000 x 40%) with lvl 10 Enshieldment, and 900 damage reduction with lvl 10 Illusion (18% x 5000). Though of course when it triggers, Illusion will reduce it by a straight amount of 5000, whereas Enshieldment only reduces it by 2000. Though Illusion triggers approximately 10 times out of every 100 attacks, and Enshieldment 66 times out every 100 attacks.

The probability favors Enshieldment even more when a multi-attack is considered. For example, with a mage’s RoF that deals 2500 each attack, Enshieldment still gives 66% chance to block the entire 5000 worth of damage. However, with Illusion, the chance to dodge both attacks is 3% (18% x 18%).

Enshieldment is the clear winner here. Please provide a counter example, with mathematical justification, if you can think of a case where Illusion is better.

Fortunately, you don’t have to pick if you don’t want to. You can equip both Enshieldment and Illusion.

Will Destroyer vs Sniper’s Edge

Sniper is almost always paired with Determination, but let’s look at the 1-to-1 comparison first.
Will increases damage dealt by 5% / lvl, Sniper adds 216 points to Critical points, which is approximately 10.2% chance to land a critical hit.

Comparing these 2 astrals is not as straight forward as the first three. All the comparisons up to now are of the “same nature”, x% chance vs x% chance, where x is always the same number of the two astrals being compared.
In this case, however, Will has 100% chance of increasing your damage dealt by 5% / lvl, whereas Sniper increases your chance to land a critical with a diminishing rate as your astral’s level goes up.

Let’s start with a straight calculation.
With lvl 1 Sniper which gives 10% chance to do critical (which is 1.5x normal damage?), and 5000 base damage, you can expect to deal 7500 damage once out of every 10 attacks.
With lvl 1 Will, you deal 250 more damage each attack, and in 10 attacks that equals to 2500 more damage.
Exactly the same!

The result changes as the astral level goes up however, because of the diminishing rate Sniper gives.
With lvl 10 Sniper, we get 66% chance to do critical. Thus we can expect to deal 7500 damage 66 times out of every 100 attacks, for a total damage of 5000 x 34 + 7500 x 66 = 665,000.
With lvl 10 Will, we get 50% additional damage each attack, for a total damage of 5000 x 100 x 1.5 = 750,000

This calculation is different when it concerns an Archer since Eye of Eagle and Battle Prowess change the critical chance and damage dealt respectively. These 2 archer passive skills alter the equation significantly enough that it may tilt the favor toward Sniper when you’re an archer. Especially when combined with Determination.

Determination vs the rest

Determination increases crit base damage by 5% / lvl.
If you don’t equip Sniper, it is generally not recommended to equip this astral. On the flip side of the coin, equipping this astral automatically takes up 2 astral spaces since the other slot is taken by Sniper.
The question then is, what other option do we have at these 2 Astral spaces if we don’t use Sniper/Determination combo? This question does not pertain an archer in most cases.

Unfortunately this is as far as my definitive guide goes. Everything beyond this depends greatly on your build and even party. Though hopefully I have helped to eliminate 2-5 options, making it easier for you to choose from the remaining.
Part 2 below offers one suggestion on astral choices. I try to be as objective as I can, but in some cases it is not possible to be completely objective, it varies greatly depending on your individual situation.

Part 2. Astral Choices

For the purpose of this guide, I will group all the astrals into 4 categories:

Core astrals are must haves.
Special occasions are nice to haves, depending on what you’re currently doing, for example Guardian Angel when you know for certain you’re facing a high crit opponent.
Defensive and offensive are what you need to choose to fill in your slots after you’ve equipped all your core astrals.

With the game’s primary focus being PvP, and PvP fights are generally shorter, my recommendation would be to choose “certain” astrals over “chance” astrals. This thought is driven by the same mathematical principle that guides financial investment strategy. At young age, you put more eggs in stocks (“chance astrals”), as you get older, you switch more and more eggs toward bonds and even cash (“certain astrals”).

Therefore, between choosing Regeneration and Brilliance, for example; even if you do an average of 6000 damage (expected heal value of 600 with Regeneration, vs a certain one-time 500 higher hp), I would still go with Brilliance.

Level 30
As mentioned, the 3 core astrals are most common, and most recommended, choices when you are under level 40. There is generally no different choices here regardless of what class you are, except for the matk vs patk.

Level 40
The path starts to diverge among the 3 classes and the individual build. One thing is true, this level is low enough that none of the “chance” astrals will not be useful yet. Therefore, I am eliminating Deflection, Regeneration, and Blessed Health.

Knight
Viable options for knights include Will Destroyer, Enshieldment, Goddess, or Brilliance.

With already naturally high HP, Brilliance will not add much (percentage-wise), that its benefit is likely to be smaller compared to other percentage-based Astrals.
I also leave Illusion out at this level since you only have 1 slot and Enshieldment is mathematically better than Illusion.

As to which one exactly you should pick depends on you skill allocation and stats. Will Destroyer depends on your average damage you dish out, while Enshieldment and Goddess depend on average damage you receive.

Let’s look at Enshieldment and Goddess. We’re interested in column 4 (average expected damage reduction from Enshieldment) and column 6 (damage reduction from Goddess) in below table.
Again, this is based on 5000 damage done to you, and no other source of +block. I also assume dodged attack reduces its damage by 40%.

Level

+Block

Chance

exp. dmg. reduction

+ %reduction

dmg. reduction

1

216

10%

205

3%

150

2

432

19%

389

6%

300

3

648

28%

554

9%

450

4

864

35%

702

12%

600

5

1080

42%

835

15%

750

6

1296

48%

954

18%

900

7

1512

53%

1061

21%

1050

8

1728

58%

1157

24%

1200

9

1944

62%

1244

27%

1350

10

2160

66%

1321

30%

1500

Enshieldment seems to be the clear winner here. Especially when the passive skill Enhanced Block is considered, which heals 4% of your HP. Even at lvl 10 where Goddess provides more damage reduction, with Enhanced Block, you only need to have a HP of more than 4500 (=(1500-1320)/4%) for Enshieldment to outperform Goddess.
However, it must also be noted that Enshieldment does not always trigger on each attack, whereas Goddess does. So you must still decide, based on your current Enshieldment level (block chance), whether you want to gamble for the much higher payouts or for the much lower, but confirmed, payouts.

You now just need to calculate your damage increase with Will Destroyer to make your decision on your fourth astral.
In general, if your pAtk is higher than your def, then go for Will Destroyer, otherwise go for either one of these damage reduction astrals.

Archer
Easy one. Sniper’s Edge. One of the 3 core astrals if you had already equipped Sniper since lvl 30.
Mage
The choices are similar to a Knight. The same analysis in the Knight’s section regarding Goddess and Enshieldment also applies here.

Unique for a Mage, Brilliance now also pushes its way into conversation, because this astral also affects Suntoria’s heal amount.

Without the lump sum 400 health bonus, Goddess only needs 800 damage to counter to benefit offered by Suntoria’ed Brilliance. In other words, if your opponent does more than 800 damage per turn to you, then you’re better off with Goddess. However the 400 health lump sum changes the equation to favor Brilliance. 800 damage is just enough to counter the 24 “heal from Brilliance”.

How much more damage is needed to counter the 400 health depends on the average duration of each fight.
Suppose each fight lasts for 7 turns on average, then for Goddess to outshine Suntoria’ed Brilliance, your opponent would have to deal at least an average damage of 2700 (=(400×0.06 + (400/7) / 0.03)

The damage received needs to be higher for shorter fights.

Level 50

This is often the crucial turning point in a toon’s life. Many toons entering this stage while they should have stayed a bit longer in the 45-49 phase. This sometimes result in people getting frustrated and leaving the game, or making others frustrated by their complaints.
Choosing the right astral goes a long way toward making or breaking your toon. The choices now also depend not only on your class, but also your overall build. What stats your items have, what kind of gems you put into their sockets, what skills you choose, all affect how you should choose your astrals.
Brilliance becomes a more viable option too since by this time you generate enough gold to level this astral up to a “usable” level.Knight
I have mathematically shown in the first part of this guide that going for Critical build is not as effective as going for the Will Destroyer path. You could, of course, compensate for the baseline inefficiency by pumping $$ into higher level Crit gems, for example.
Therefore, the choices here are the same as lvl40, pick whatever you left off at level 40. 2 of Will Destroyer, Enshieldment, or Goddess Blessing. Though I’d say that Illusion can re-enter the picture as a potential for your fifth slot.Archer
Another easy one. Determination, to go along with the Sniper that you’ve picked up at level 40.

Mage
Similar to a Knight’s choices, pick what you left off as viable options at level 40.

Level 60+

One thing left to compare is the “chance” astrals. Technically, Enshieldment and Sniper also belong in the “chance” astral group. However, since Enshieldment has been discussed to death, you can always refer to earlier analysis to compare that with other “chance” astrals discussed here. For what it’s worth, Sniper has the same calculation as Enshieldment.

Deflection reflects damage received by 10% / level. While Regeneration heals 10% / level of damage dealt. Each has a 10% trigger rate.

This 10% trigger rate is the deal breaker for these 2 chance astrals. While it may be ok (and in fact could be great) for PvE, PvP fights are too short for this to trigger. This only happens 1 out of every 10 attacks. If a fight lasts for 5 rounds (which is a typical length of Group Arena), you can expect either of these astrals to trigger every other fight. In other words, you go without astral during one out of every two fights.